Oscillating system



Nov. 16, 1948.

P. F. BROWN OSCILLATING SYSTEM Filed Jan. 11, 1944 All...

FIG-2 INVENTOR. PAUL F BROWN [#forng,

Patented Nov. 16, 1948 7 OSCILLA'TING SYSTEM Paul F. Brown, Cambridge,Mass,, assignor, by mesne assignments, to the United States of Americaas represented by the Secretary of War Application January 11, 1944,Serial No. 517,895

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

This invention relates to "an oscillating system and more particularlyto an oscillator for generating a predetermined number of cycles. In theuse of certain equipment, it is frequently desirable to generate apredetermined number of cycles and thereafter suppress said oscillationsuntil a new cycle of operation is initiated. Thus in certain types ofradio apparatus the pulsing of a transmitter is utilized to initiate atrain of waves. In the use of an ordinary oscillator, it is necessary tobuild up the initial cycles to the final amplitude. When the negative orzero resistance of the oscillating system becomes a positive resistance,then damping sets in to produce a train of waves of decreasingamplitude. However, in certain instances it is necessary to haveoscillations begin practically instantaneously at substantially fullamplitude, maintain the oscillations at substantially constant amplitudefor a predetermined number of cycles and then suppress the oscillati-onsalmost instantaneously.

In its more general aspect, the invention provides a shock-excitedoscillating circuit having a minimum of damping during the time thatoscillations are desired. When the number of waves generated has reachedthe required value, means are provided for introducing high damping.Unless the shock duration is small compared to the periodicity of thewave train,'there will be a masking effect on the initial cycles andthis will effectively result in the train beginning several cycles afterthe desired time. A small shock duration requires a high shock intensitycompared to the energy in a wave train of a naturally resonating system.But high shock intensity involves forced oscillations and transientefieots which will have a deleterious effect on the wave shape of thetrain. This invention provides means for impressing a comparatively highintensity shock on a resonant circuit and provides means for eliminatingshock effects in the circuit so that substantially pure naturalresonance efifects result.

Referring now to the drawings, Figure 1 shows one circuit wherein acombination of inductance and capacitance .are used in connection with acrystal. Figure 2 shows a modification wherein resistance andcapacitance are used in combination with a crystal.

Referring now to Figure 1, a vacuum tube 10 is provided having a cathodeH connected 12 Claims. (01. 250-36) through a bias resistor I2 to groundl3. An input terminal I5 is connected to cathode II. and together withground l3 forms an input circuit. Control grid I6 of tube It! isconnected by a grid resistor I! to ground I3. An accelerating grid I8 isconnected through a resistor l9 to junction point and thence through adropping resistor 2! to lead 22 connected to a source of 3+ potential.Accelerating grid [8 is effectively grounded as'far as alternatingcurrent is concerned by condenser 23.

Vacuum tube It) has its anode 25 connected through a load resistor 26 tojunction point 20. Shunted across resistor 2B.are condenser 21 andwinding 28, forming the primary of a transformer 29. Transformer 29 hasa secondary, having ,a center connection '3I connected to ground througha variable resistor 32. The terminals of secondary 30 are connected tovariable condenser 33 and crystal 34 respectively, these latter going toa junction point 35. Load resistor 26 preferably has a resistance highcompared to the impedance of the resonant circuit 2'|2B for theoperating frequency.

The entire secondary circuit forms a bridge system in which excessiveshock energy tending to cause forced'oscillationsqis dissipated. Theenergy left for normal resonance operation remains in the circuit,which, after the initial shock, behaves as a normal resonant circuit.The crystal with its high Q results in the overall circuit Q being highenough so that a wave train of substantially constant amplitude isgenerated. The response of a crystal to a shock is highly destable inthis instance. The crystal appears to follow the shock wave and thencontinues on with oscillations upon the disappearance of the shock. Theinherent sharp frequency response of this type of circuit is desirablesince transients are suppressed.

Junction point 35 is connected through a coupling condenser 36 to grid31 of vacuum tube 38. Grid 31 is connected to ground through a gridresistor 39, while cathode 40 is directly connected to ground. Anode 4|of vacuum tube 38 is connected through a load resistor 42 and droppingresistor 43 to lead 22.

Anode 4| of tube 38 is connected by lead 45 and coupling condenser 46 tocontrol grid 41 of vacuum tube amplifier 48. Control grid 41 has a gridresistor 49 connected between it and ground. Cathode 50 is alsogrounded. Vacuum tube 48 has its anode 5! connected through a loadresistor 52 to the junction of resistors 42 and 43 and is lay-passedbygrounded. condenser 53.

From anode 5I a lead 55 is taken, terminating in an output terminal 56which together with ground constitute an output circuit.

From anode M of vacuum tube 38 lead 45 is extended to a couplingcondenser 51, and the other terminal of this coupling condenser isconnected to control grid 58 of vacuum tube amplifier 59. Control grid58 is connected to ground by means of grid resistor 69, while cathode 6|is automatically biased by bias resistor 62 connected between it andground. Bypass condenser 63 is shunted across bias resistor 62.Accelerating grid 65 is by-pas-sed to ground by condenser 66 and ismaintained at a suitable potential by connection to lead 22 throughdropping resistor 61. Vacuum tube 59 has its anode 88 connected througha load resistor 19 to dropping resistor 61 and thence to lead 22. Loadresistor I9 is shunted by condenser II and the primary I2 of transformerI3. Transformer I3 has its secondar-y M shunted-by a condenser I5. Oneterminal -16 of condenser L-is connected to ground by lead 'IJ, thislead also being connected to suppressor.'grid 18 of the vacuum tube. Theother terminal 89 of condenser I5is connected to lead 81 :going back tocontrol 'grid I6 of the first vacuum tube. -A feed-b-ack controlresistor 82 is connected between lead BI and ground.

"The-operation of the system is as follows. A

positive gate input consisting of a rectangular voltage Wave of suitableamplitude and duration is impressed between .ground and input terminaland-serves to raise the potential of cathode I I. -"As'shown, vacuumtube I 9 isnormally conducting but is rendered non-conducting at theinstant that' the 'catho'de potential is-raised by the control gate.lI-he'cutting off ofspace current in vacuum 'tube .19 results in ariseinpotential at'anode 25, and .thisgeneratesasurge across condenser 21:anmprimaryL-ZS. The surge in primary 28induces a surge insecondary 39,and this results in shock exciting the crystal abridge circuit. Durinthe idiirationof the positive gat.e,'vacuum tube I9 is non-conducting sothat the crystal circuit may nscillate with a minimum of damping. Thisis :du'e to-the'high resistance of. The shock-itself is 'eliminated bythe bridge circuit. The sine waves generatedlin :the crystal bridgecircuit are impressed-through.coupling condenser 36 on'control grid31=of'vacuumtube-'38, amplified and impressedon control grid '4I-ofamplifier '48. The resulting potential variations at anode 5| of vacuumtube 48 are impressed upon output terminal'5li.

Atthe same time,wavesfrom-anode4I are also i impressed-upon control grid58 of amplifier 59 and 'result in oscillations being generated incircuit-TI and -12. These amplified waves appear in secondary I4 and arefed backto control grid I6 of first vacuum tube I9. The amplitudeo'ffeedback may-be controlled-by variable resister 82. As long'as vacuumtube-l9is non-conductingand thisoccurs during the'duration of thepositive gatefee'd-'backto control grid I6 is ineffective. By-carefuldesign of the'various circuits, a substantially uniform calibratedseries of waves may be taken off at output terminal'56. At the end of*the positive gate when cathode II drops, vacuum'tube I9 becomesconducting. This provides substantial damping for thecrystal bridgecircuit while the'feed back, which is 180out of phase,'adds'further-damping. The 180 phase angle-of feed-"back is acomposite-of the phase angles incircuit 21- 28, tube circuitsand otherelements. Thus" phase shift due to'initial crystal response and otherunavoidable circuit elements are compensated for. The net result is thatwhen the positive ate is ended, oscillations in the crystal bridgecircuit are quickly suppressed. Thus the inverse feed-back potentialapplied to the bridge circuit functions to accelerate the damping.

In the system shown in Figure 1, the resonant circuit formed bycondenser '21 and primary 28 does not introduce much damping resistanceinto the secondary crystal circuit. This will be true as long as loadresistor 26 is high and vacuum tube I9 is non-conducting. As soon asvacuum tube I9 becomes conducting, then a comparatively low resistanceis effectively connected across primary 28 and results in a highlydamped primary circuit. This high damping is coupled into the crystalcircuit.

Referring now to Figure 2, a circuit is disclosed havin a differentoperation. In this circuit, a vacuum tube 99 has its cathode 9|connected through a high bias resistor 92 to a ground lead 93. Controlgrid 94 is connected through a grid resistor 95 toground. Vacuum tube 99has its anode 96 connected through a load resistor 91 and a droppingresistor 98 to alead 99 connected to a suitable source-of B+ potential.The junction of resistors 91 and 98 is connected to .a groundediby-passcondensor I09.

From anode 96 of vacuum tube :99 connection is made to a condenser I Mand thence by lead I112 to Ia variable tuning condenser I03. Fromcathode v9I a connection is taken through a condenser I94 and'lead I95to crystal I196. A lead I91 connects crystal I96 and variable condenser193. Between leads I92 andI95 a high resistance I98 is connected andcooperating with this resistance is a. grounded movablecontact I99.Condensers I..9I and I94 may have substantiall equal capacitances, whilevariable condenser I93 may preferably have a capacitance range somewhatlarger than but of the order of the capacitance of crystal I96.

From lead I91 aconnection is made to control grid II9'of a vacuum tubeamplifier III having a cathode I IZcOnnected-through a comparatively lowbias resistor II3 to ground. Control grid 119 is connected to ground bya high grid re- .sistor ,I'I5. Anode I I6 is-connected toa'parallelresonant circuit consistingof condenser II! and inductance I. I.9,-andfthence-the anode circuit continues on throughadroppingresistor I29tolead .99. A by-passcondenser I.2-I is connected between ground and the-low-end .of dropping resistor Ir29. Variations in potential of the.anode II6 are impressed upon a "coupling condenser I22 and continueonto control grid 123 of vacuum'tube amplifier .-I24. The gridcircuit iscompleted bya grounded .grid resistor I25, While'cathode1I26 isconnected to ground by -.a .low bias resistor -I- 2'I. .Anode -I28 is.connected through a load resistor .li29 and dropping'resistor I39 toB+-lead 99. A .byepass condenserd 3 I .is connected between droppingresistor 13.9;and ground. An output terminal I32.is taken fromanode I28andtogether with ground constitutes an outputcircuit.

From anode I28 connectionismade to a con plingcondenser I23 and thenceto agrounded resistor I34. Cooperating with resistor I34 is apotentiometer tap.I35 connected to .control grid I36of an amplifier I31.Cathode I38 is connected .to'groun'd'by .a low bias resistor I39.Anacce'l- 'eratinggrid I49 is .connected through a suitable resistor I4Ito a dropping resistorl'42 and thence to B+lea'd-9.9. Grounde'd'by-passcondensers I43 and I4-4'are provided on opposite sides of resistor MI. Asuppressor grid I45 maybe grounded, while anode I46 is connected througha load resistor I41 to dropping resistor I42. From anode I45 a feedbacklead I56 is takenthrough a coupling condenser II, lead i561 going backto con--- trol grid 94 of vacuum tube 96. Input terminal I52'isconnected to cathode I36 and together with ground forms an inputcircuit.

Pentode I31 is biased by potentiometer tap I35 to be normallyconducting. When a positive voltage gate is impressed on input terminalI52 .and ground, the potential of cathode I38 is raised with respect tocontrol grid I36 and results in space current being cut off. Thisresults in a sudden rise in potential at anode I46, which rise iscommunicated to control grid 94 of vacuum tube 90. This tube has a highbias resistor 92 in the cathode circuit which results in little spacecurrent under normal conditions. However, the high positive voltage gateimpressed upon control grid 94 reducesthe resistance of vacuum tube 86to a low value. The sudden decrease in tuberesistance and increase inspace current cause the potential at anode 96 to drop sharply and thusshocks the bridge circuit IBI, Hi3, I06 and I04.

As long as thepositive gate is impressed upon control grid 94, vacuumtube 90 forms a comparatively low resistance connection betweencondensers I04 and i8! and completes the crystal circuit. Resistance I03is so high in comparison to the series react-ances of condensers MI andI84 for the frequency used and resistance of tub-e 90 as to havesubstantially no effect. The shock impressed upon crystal lUB results inthe generation of a series of sine waves having a comparatively lowdecrement. These sine waves are'impr-essed upon amplifier III and resultin oscillations in parallel resonant circuit I H and I I8,.- Thiscircuit is tuned to the same frequency as generated in theshockeXcited-crystal circuit. From vacuum tube I I! the sine waves arefurther amplified at vacuum tube I24 from which the output may be taken.

In order to provide feed-back for suppressing oscillation after the gatedisappears, the output from vacuum tube I24 has a predetermined portionthereof applied to the control grid of pentode I3'I. As long as thepentode is cutoff by the gate there is no feed-back. At theend of thepositive gate at input terminal I52, vpentode I31 reverts to its normalconducting condition. Then feed-back in opposite phase is applied totube 90. At the same time that pentode I31 resumes its normal conditionof conductivity, a negative pulse is impressed upon control grid 94 ofvacuum tube 98 and causes that tube to be near cut-off. When thishappens, there is a high resistance between condensers IllI and I04 byway of vacuum tube 90. Also feed-back eifectively increases thisresistance. This leaves the crystal circuit highly clamped by resistanceI 08.

Vacuum tube amplifier I II in the absence of signals on its control gridII 0 tends to be normally conducting by virtue of a comparatively lowvalue of bias resistor II3. Hence the comparatively low resistance ofvacuum tube III becomes shunted across the parallel oscillating circuitnormally consisting of condenser I I! and I I8,

of the circuits will depend on such factors as the number of cycles foreach gate cycle, permissible decrement, variation of circuit constantswith tube life and other details. If a large number of cycles per shockexcitation are required then high Q crystal circuits will be required,care will have to be exercised in coupling through transformers orcondensers and the entire system will have to be designed to have a lowdecrement. In addition, when damping is introduced, it will have to beheavy to dissipate the oscillating energy. However, such details arewell known to one'skilled in this art.

What is claimed is:

1. An oscillating system comprisin a resonant circuit having inductanceand capacitance, said circuit having some resistance inherent therein,means for shock exciting said circuitso that oscillations are inducedtherein, an output circuit from which said oscillations may be taken forutilization, and means operative after a predetermined number ofshock-excited oscillations for damping said oscillations, saidoscillating circuit having negligible damping during its normaloperation and having such high damping upon the operation of said lastnamed means as to suppress oscillations completely almost instantly, anamplifier for said shock-excited oscillations, means for feeding saidamplified oscillations back into said shock-excited circuit in oppositephase, and means for rendering said feed-back means inoperative duringthe time that oscillations are desired.

2. An oscillating system comprising a parallel resonant circuit havinginductance and capaci- This results in a high dampin of oscillations inI tance, and including a crystal, said circuit normally having a lowdecrement, a vacuum tube amplifier, said amplifier having cathode, gridand anode circuits, means for connecting said resonant circuit in saidanode circuit, said anode circuit forming a low resistance across saidres.- onant circuit when said tube is conducting, means for norm-allymaintaining said Vacuum tube amplifier in a conducting condition, meansfor changing said vacuum tube from a conducting condition to anon-conducting condition rapidly enough to shock excite said resonantcircuit, means for maintaining said vacuum tube in a non-conductingcondition for the time during which oscillations are desired, and meansfor returning said tube to its normal conducting condition whereuponsaid oscillating circuit becomes highly damped to suppress oscillations.

3. The system of claim 2 wherein oscillations from said parallelresonant circuit are fed back to the grid of said amplifier, saidfeed-back being ineffective while said tube is non-conducting and beingout of phase so that when said tube becomes conducting amplifier actionin the tube aids in damping.

4. An oscillating system comprising a three element vacuum tube, threecondensers and a crystal all connected in series to form a bridge with acrystal in one arm a condenser in a second arm the third and fourth armshaving condensers with the cathode-anode tube space forming a switchconnection between the third and fourth arms, a high damping resistanceconnected across the first and second arms, said bridge being resonantto a certain frequency when said tube is conducting, said dampingresistance being high enough to have little effect on the bridge undernormal conditions, means for biasing the tube grid so that said tube isnormally near cut-off,

means for sharply changing said grid bias to render said tube highlyconducting and shock excite said bridge circuit, means for maintainingsaid tube in said highly conducting condition while oscillations aredesired and means for restoring said tube to its normal non-conductingcondition to suppress oscillations.

5. The system of claim 4 wherein oscillations from said crystal circuitare fed back to the control grid of said amplifier, said feed-back beingout of phase to suppress oscillations.

6. An oscillating system for generating spaced wave trains comprising acrystal bridge circuit, means for intermittently shock exciting saidbridge circuit, means for dissipating the initial shock in said bridgewhile leaving energy therein for resonant oscillations, and means foramplifying said resonant oscillations without imposing a substantialload on said resonant circuit.

7. The system of claim 6 wherein the amplified oscillations are fed tosaid resonant circuit 180 out of phase and means for rendering saidfeedback inoperative only during the time that oscillations are desired.

8. An oscillating system comprising a symmetrical bridge, only one ofthe arms of said bridge comprising a circuit resonant to a predeterminedfrequency and having a relatively low decrement at said frequency, theother arms of said bridge, being so constructed that said bridge issubstantially balanced at all frequencies except those near saidpredetermined frequency, means for applying intermittent, shock-excitingpulses to the input of said bridge, the repetition rate of said pulsesbeing considerably lower than the resonant frequency of said circuit,whereby the initial shock of each pulse is substantially balanced out,while the resonant circuit continues to oscillate at its own frequencyafter said initial shock.

9. An oscillating system comprising a symmetrical bridge, only one ofthe arms of said bridge comprising a circuit resonant to a predeterminedfrequency and having a relatively low decrement at said frequency, theother arms of said bridge, being so constructed that said bridge issubstantially balanced at all frequencies except those near saidpredetermined frequency, means for applying intermittent, shock-excitingpulses to the input of said bridge, the repetition rate of said pulsesbeing considerably lower than, and independent of, the resonantfrequency of said circuit, whereby the initial shock of each pulse issubstantially balanced out while the circuit continues to oscillate atits own frequency after said initial shock, and means to damp saidoscillations a predetermined interval after each shock.

10. A system as set forth in claim 9, wherein said last named meansapplies an inverse feedback potential to said circuit.

11. The method of generating spaced wave trains which comprisesintermittently shock exciting a resonant circuit, alternately shuntingsaid circuit with a low impedance to damp the waves therein, andaccelerating said dampingby applying inverse feed-back to said circuitduring the shunting periods.

12. The method of generating spaced wave trains comprising shockexciting at spaced intervals a resonant means to cause it to generateoscillations to be utilized, alternately damping said resonant meansreversing the phase of said oscillations, and applying the oscillationsof reversed phase to said resonant means during each damping period.

PAUL F. BROWN.

REFERENCES CITED The following references are of record in the

